1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device having a field plate structure.
2. Background Art
Japanese Laid-Open Patent Publication No. 2005-093864 discloses a method of manufacturing a semiconductor device, which includes forming an insulating film on a portion of the surface of a semiconductor layer and then forming a metal layer continuously extending on the surface of the semiconductor layer and on the surface of the insulating film. This semiconductor device manufacturing method performs both an exposure/development step for processing the insulating film into the desired shape and an exposure/development step for processing the metal layer into the desired shape (the latter step being hereinafter referred to as the “metal film exposure step”). The portion of the metal layer overlying the semiconductor layer functions as a gate electrode, and the portion of the metal layer overlying the insulating film functions as a field plate.
In the method for forming the field plate, an opening is formed in the insulating film, and the metal layer is formed to continuously extend over the opening and on the surface of the insulating film (covering the exposed portion of the semiconductor layer at the opening). The field plate (i.e., the portion of the metal layer overlying the insulating film) should preferably be formed at a predetermined position relative to the center of the opening. It has been found, however, that the position of the field plate structure relative to the center of the opening may vary due to variations in the metal film exposure step, resulting in variations in the characteristics of the semiconductor device.